During this century, modern society has been successful in controlling infectious disease by, for example, using vaccines, using drugs (such as antibiotics), and using strict public health measures. These advances have been paralleled by successfully identifying the causative agents of infectious disease, which agents include bacteria, fungi, protozoa, and viruses. Thus, aside from a healthy host immune response, antibiotic therapeutic regimens now represent the primary course of treatment for most infectious diseases in developed countries. In contrast, infectious diseases remain a serious concern for developing countries, due to the lack of adequate sanitation and consequent poor hygiene, and for immunocompromised individuals. However, due to the widespread use of antibiotics, drug-resistance to one or more antibiotics is becoming an increasingly common problem all over the world for controlling a number of previously treatable infectious diseases (e.g., Staphylococcal infections). Accordingly, treatment of nosocomial infections (i.e., those arising in hospitals) and infections related to indwelling medical devices is becoming more difficult because of the intractable nature of infections due to drug-resistant microorganisms, which is a serious and world-wide clinical concern.
A variety of artificial devices to assist in the performance of various physiological functions have been developed to be inserted into the human body for short periods, such as catheters, or to be inserted permanently, such as artificial heart valves; however, the interface between the device and body creates new biological conditions that increase the propensity of infection. For example, catheter-associated infections may have multiple potential sources of contaminants, including contaminants in the infusate that is directly injected, contaminants of the catheter hub where the administration set attaches to the catheter, contaminants carried hematogenously from remote sources of local infection to colonize the catheter, or contaminants of cutaneous origin that invade the percutaneous tract extralumenally at the time the catheter is inserted or in the days following insertion. Available evidence indicates that the majority of catheter-related bacteremias originate from the cutaneous microflora of the insertion site. Given the evidence for the importance of cutaneous microorganisms in the pathogenesis of intravascular device-related infections, measures to reduce colonization of the insertion site are of great importance in the health care industry.
Another clinical indication of importance is nosocomial infections and, in particular, nosocomial pneumonia and nosocomial sinusitis. Contaminated secretions may be aspirated daily in the tracheobronchial tree, which may lead to pneumonia. Additionally, the risk of nosocomial pneumonia is increased after a tracheostomy is performed and during prolonged endotracheal intubation. Sinusitis has been found to be associated with an increased risk of nosocomial pneumonia, presumably due aspiration of contaminated sinovial fluids into the distal airways. Sinusitis typically arises in the hospital setting among mechanically ventilated patients. Recommended treatments for sinusitis of intubated patients, include removal of the tubes or systemic antibiotics. However, once again, the increase in antibiotic-resistant organisms makes the latter treatment, whether preventative or curative, less efficacious.
Yet another clinical indication, although not life-threatening, is the most common skin disease of adolescence and early adulthood, acne vulgaris, or acne as it is generally called. In addition to psychological effects, such as anxiety, depression and withdrawal from society, studies have also shown that acne vulgaris can directly and significantly affects a patient's quality of life. Antibiotic agents have been extensively used for the treatment of acne for several decades; however, there is a growing concern that with the use of antibiotics to treat acne, drug-resistant microorganisms will inevitably emerge.
To address the issue of ever increasing drug-resistant microorganisms, investigations have turned to new classes of antibiotics, such as antimicrobial peptides. Antimicrobial peptides are found in evolutionarily diverse species including, for example, prokaryotes, plants, insects, and mammals. Antimicrobial peptides may be anionic, but most known antimicrobial peptides are cationic. Multiple families of antimicrobial cationic peptides are known and these peptides encompass a wide variety of structural motifs, yet all of these cationic peptides have similar physicochemical properties. For example, most known antimicrobial cationic peptides are cationic at neutral pH, are generally less than 10 kDa, and are amphipathically “sided” in solution such that hydrophobic side chains are regionalized. Many antimicrobial cationic peptides are known, including defensins, cecropins, melittins, magainins, indolicidins, and protegrins. The advantages of cationic peptides are their ability to kill target cells rapidly, their broad spectrum of activity, and their activity against some of the more serious antibiotic-resistant and clinically relevant pathogens. Most, importantly, antimicrobial peptide-resistant, microorganisms are relatively difficulty to select in vitro. However, some antimicrobial peptides have been found to be toxic (e.g., bee venom, wasp venom, and scorpion toxin), some have been found to have reduced activity in vivo (due to factors such as high mono- and divalent cation concentrations, polyanions, serum, apolipoprotein A-1, serpins, and proteases, although many peptides are not affected by these factors), and some have been found to be less potent than conventional antibiotics.
Hence, a need exists for identifying modified or derivative antimicrobial peptides with improved activity (and in some cases with reduced toxicity), for formulating such peptides and derivatives thereof for optimal therapeutic use, and for developing therapeutically effective clinical regimens for these cationic peptides. Furthermore, there is a need for formulations that are useful in a variety of clinical indications. The present invention meets such needs, and further provides other related advantages.